1. Field of the Invention
The present invention relates to an information processing apparatus, an information processing method, and an information processing computer program product for performing a mutual authentication process by using key management information that can be updated to invalidate illegitimate devices and/or illegitimate storage media.
2. Description of the Related Art
Conventionally, a content protecting technique called Content Protection for Recordable Media (CPRM) has been applied to SD Memory cards (SD cards), as a mechanism to protect the contents that are written to and read from the SD cards. Also, authentication methods are used as a mechanism to write and read management information to and from SD cards, the management information including, for example, encryption keys used in encrypting processes to protect the contents. In addition, a technique that uses key management information called Media Key Block (MKB) as a mechanism for invalidating illegitimate devices is applied to SD cards. In this situation, illegitimate devices include devices that remove the protection that is realized by a content protecting technique and applied to contents, devices that tamper with contents, and devices that are capable of tampering with contents. The key management information is management information used for disabling illegitimate devices from decrypting encrypted contents stored in storage media such as SD cards (i.e., for invalidating the illegitimate devices or eliminating the illegitimate devices), the illegitimate devices being recognized as illegitimate devices at the time when the key management information is issued by a technical license organization. More specifically, the key management information contains a plurality of encrypted media keys each of which is obtained by encrypting a specific media key by using a different one of a plurality of device keys. The media key is key information used in an authentication process that is performed between a device and a storage medium that communicate with each other. The device key is key information uniquely assigned to each of the devices. At least one device key is stored in each of the devices. When new key management information that invalidates the media key decrypted with the secret key has been generated and a mutual authentication process is performed by using the new key management information, illegitimate devices will fail the authentication process. Thus, it is possible to invalidate the illegitimate devices. Accordingly, the key management information used in this situation needs to be the most updated one that reflects the information of the illegitimate devices that are known to be illegitimate at the point in time when the storage media are manufactured. Otherwise, it is not possible to implement the illegitimate device invalidating process in a proper and efficient manner. Thus, a mechanism has been introduced to SD cards so that the key management information can be updated with newer information.
Unlike magnetic optical disks such as Digital Versatile Disks (DVDs), SD cards have a controller built therein, in addition to a flash memory used for storing data. The controller performs a mutual authentication process with an information processing apparatus so that only legitimate devices (i.e., devices that are not illegitimate devices) are able to write and read data, such as the encryption keys and the key management information, to and from the SD cards. On the other hand, a content protecting technique called Advanced Access Content System (AACS) is applied to High Density DVD (HD DVDs) and Blu-ray Disks (see, for example, Advanced Access Content System (AACS) (http://www.aacsla.com/specifications/specs091/AACS_Spec_Common—0.91.pdf)). This technique uses key management information that has the same purpose and the same name as the MKB described above but has a completely different data structure.
In actuality, however, even with the content protecting techniques implemented in CPRM or AACS, it is not easy to invalidate storage media that have illegitimately been manufactured. For example, although it is possible to invalidate devices and storage media that have illegitimately been manufactured by identifying the secret key stored in each of the storage media, it is, in fact, difficult to identify the secret key stored in each of the devices and the storage media that have illegitimately been manufactured. As a result, a method for efficiently invalidating devices and storage media that have illegitimately been manufactured has been in demand.